We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6–160 \mu m from the SINGS project .
The availability of the 1.1 mm map enables us to measure the long–wavelength tail of the dust emission in each galaxy , and in sub–galactic regions in NGC 1512 , and to derive accurate dust masses .
The two galaxies form a pair consisting of a large , high–metallicity spiral ( NGC 1512 ) and a low metallicity , blue compact dwarf ( NGC 1510 ) , which we use to compare similarities and contrast differences .
Using the models of Draine & Li ( 8 ) , the derived total dust masses are ( 2.4 \pm 0.6 ) \times 10 ^ { 7 } M _ { \odot } and ( 1.7 \pm 3.6 ) \times 10 ^ { 5 } M _ { \odot } for NGC 1512 and NGC 1510 , respectively .
The derived ratio of dust mass to H i gas mass for the galaxy pair , M _ { d } / M _ { HI } \sim 0.0034 , is much lower ( by at least a factor of 3 ) than expected , as previously found by Draine et al .
( 9 ) .
In contrast , regions within NGC 1512 , specifically the central region and the arms , do not show such unusually low M _ { d } / M _ { HI } ratios ; furthermore , the dust–to–gas ratio is within expectations for NGC 1510 .
These results suggest that a fraction of the H i included in the determination of the M _ { d } / M _ { HI } ratio of the NGC 1512/NGC 1510 pair is not associated with the star forming disks/regions of either galaxy .
Using the dust masses derived from the models of Draine & Li ( 8 ) as reference , we perform simple two–temperature modified–blackbody fits to the far–infrared/mm data of the two galaxies and the sub–regions of NGC 1512 , in order to derive and compare the dust masses associated with warm and cool dust temperature components .
As generally expected , the warm dust temperature of the low–metallicity , low–mass NGC 1510 ( T _ { w } \sim 36 K ) is substantially higher than the corresponding warm temperature of the high–metallicity spiral NGC 1512 ( T _ { w } \sim 24 K ) .
In both galaxies ( albeit with a large uncertainty for NGC 1510 ) , our fits indicate that a substantial fraction ( > 93 % ) of the total dust mass is in a cool dust component , with temperatures \sim 14–16 K for NGC 1512 and \sim 15–24 K for NGC 1510 .
This result is similar to what is determined for a few other nearby galaxies .
In contrast , the warm dust component in the sub–galactic regions of NGC 1512 represents a much larger fraction of the total dust content , in agreement with the fact that all three regions have higher specific star formation rates than the average in the galaxy ; in the center , the warm dust represents about 40 % of the total , while in the arms the fractions are close to \sim 20 % .